Me too! Bluetooth or other antennas is a possibility, but I'd like to look at using computer vision, but using a database of images stored with coordinates instead of markers. Garbos

System type

Should this work in a restricted special space (playing board) or "anywhere" in the room? Should it be 2D or 3D? How "high" a precision (cm, mm)?

What system to use? I can think of:

Broadcast signal on at least three towers, receiver in moving item that does GPS-like triangulation, ie. timing differnces. Would work wth sound rather than light/radio. (Simple speaker/microphone - cheap enough)

Don't you need 4 towers if you only have timing differences? You would also need to place the probe in time (or, as an alternate perspective, you only get relative distances, you need a fourth to make them absolute).

With sound, you might want to look in to how OLPC does this. Their problem is that there is an unknown lag between the sound command is issued and when the sound is made. Their solution is that the "tower" listens to the sound as well. IIRC, the chain of events is something like: 1. Tower sends sound. 2. Tower hears tower sound (event T1) 3. Probe hears tower sound (event P1) 4. Probe sends sound 5. Probe hears probe sound (event P2) 5. Tower hears probe sound (event T2). T2-T1 is the twice the sound travel time plus the probes reaction time, P2-P1 is the probes reaction time, so ((T2-T1)-(P2-P1))/2 is the sound travel time. All precision measuring is done locally, and only on one channel (the microphone). Actually, this might also be a good idea for radio as well, it removes the need for absolute timing, and I figure investing in 3 atomic clocks is out of the question (I know someone who has three atomic clocks and don't use them, but convincing him to borrow them to labitat might be hard).